Methods of and apparatus for irradiation of articles by radioactive panels

ABSTRACT

Method and apparatus for the irradiation of containers and articles therein, by radioactive panels. A chamber defined by shielded top, bottom and sidewalls, and one end wall, supports a radioactive panel in vertically-erect position midway between and parallel with the sidewalls, to define two corridors side by side. The otherwise open end of the chamber is closed by a cylindrical housing rotatable about its vertical central axis. The housing has four compartments separated and defined by shielded walls. In one of two 180* positions of the housing, two of these compartments register with the respective corridors while the other two face outwardly for loading and unloading. In a second 180* position the locations of the compartments are reversed. Conveyor means support the containers and move them in and along one corridor, past the radioactive panel, translate them without rotation at and along the end wall, then in a return translation pass in and along the corridor at the other side of the panel, to thus complete a cycle. Opposite sides of each container are thus directly and equally exposed to radiation, during a cycle. The bottom wall of the chamber has an opening into which fits a shielded housing for enclosing the panel during transport. Means are provided for elevating the panel from the housing into the chamber, through the opening, when the chamber and housing are in interfitting relation. The panel may be in upper and lower sections and connected for relative vertical translation. When collapsed, the panel sections fit snugly into the housing. When moved from the housing into the chamber, the sections automatically move vertically and relatively and when fully emplaced in the chamber, form what is in effect a single panel of double the area of the sections. Suitable safety interlocks provide complete protection for operating personnel and indicate and assure proper functioning of the apparatus. The invention is of particular value because it may be transported in sections from one place of use to another.

United States Patent [72] Inventors Pierre Balanca Neuilly-sl-Seine; Georges Frignet, Paris; Rene Pierlas, Antony, Seine, France [21] Appl. No. 510,863 [22] Filed Dec. 1, 1965 [45] Patented Feb. 23, 1971 [73] Assignee Saint-Cobain Techniques Nouvelles Courbevoie, France [32] Priority Dec. 2, 1964, Oct. 27, 1965, Oct. 27, 1965 [33] France [31] 997,132, 36,417 and 36,418

[54] METHODS OF AND APPARATUS FOR IRRADIATION OF ARTICLES BY RADIOACTIVE PANELS 21 Claims, 11 Drawing Figs.

[52] U.S. Cl 250/52, 250/ 106 [51] Int. Cl HOlj 37/20 [50] Field of Search 250/52, 106, 106 (SC); 99/214, 217

[56] References Cited UNITED STATES PATENTS 3,142,759 7/1964 Jefferson et a1 250/52 FOREIGN PATENTS 970,074 1/ 1962 Great Britain 250/52 ABSTRACT: Method and apparatus for the irradiation of containers and articles therein, by radioactive panels. A chamber defined by shielded top, bottom and sidewalls, and one end wall, supports a radioactive panel in vertically-erect position midway between and parallel with the sidewalls, to define two corridors side by side. The otherwise open end of the chamber is closed by a cylindrical housing rotatable about its vertical central axis. The housing has four compartments separated and defined by shielded walls. In one of two 180 positions of the housing, two of these compartments register with the respective corridors while the other two face outwardly for loading and unloading. In a second 180 position the locations of the compartments are reversed. Conveyor means support the containers and move them in and along one corridor, past the radioactive panel, translate them without rotation at and along the end wall, then in a return translation pass in and along the corridor at the other side of the panel, to thus complete a cycle. Opposite sides of each container are thus directly and equally exposed to radiation, during a cycle. The bottom wall of the chamber has an opening into which fits a shielded housing for enclosing the panel during transport. Means are provided for elevating the panel from the housing into the chamber, through the opening, when the chamber and housing are in interfitting relation. The panel may be in upper and lower sections and connected for relative vertical translation. When collapsed, the panel sections fit snugly into the housing. When moved from the housing into the chamber, the sections automatically move vertically and relatively and when fully emplaced in the chamber, form what is in effect a single panel of double the area of the sections. Suitable safety interlocks provide complete protection for operating personnel and indicate and assure proper functioning of the apparatus. The invention is of particular value because it may be transported in sections from one place of use to another.

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METHODS OF AND APPARATUS FOR IRRADIATION F ARTICLES BY RADIOACTIVE PANELS This invention relates to a method and apparatus for the irradiation of 'products or articles by exposure to a radioactive source.

It is the chief object of the invention to provide a method and apparatus which enable objects or products to be treated or irradiated with a dosage sufficiently uniform and in a time sufficiently short for commercially satisfactory and practicable use.

It is a further object to provide an apparatus as aforesaid which is of relatively light weight in comparison with the irradiating power which it affords.

Another object is to provide an apparatus of the type described which, by reason of its compactness and relatively low weight, is particularly well adapted and useful in mobile or vehicular form, as in situations where the apparatus is to be moved from place to place.

Another object is the provision of an apparatus which is operated without danger to attending personnel, efficient and accident free in use, which provides a uniform dosage of irradiation to materials or objects treated with radioactive material of medium or low power and which is a material advance in the art.

The apparatus in general comprises an enclosed shielded chamber containing a radioactive source, and mechanism for introducing into the chamber, articles or products to be irradiated and for translating or circulating these articles within the chamber so that they are uniformly and sequentially exposed to the aforesaid source.

Prior art devices for the introduction into and removal from an irradiation chamber of products to be irradiated, and enclosed in packages or containers, require moving the packages through a labyrinth or tortuous entrance and exit passageway, such that radiation from the source within the exposure chamber cannot escape to the exterior to a degree which will endanger operating personnel.

Such prior art constructions require a weight of sheathing such as lead, which is very high with relation to the power of irradiation of the source material. Such constructions are particularly undesirable in installations which are required to be mobile, that is, to be moved from place to place as from one laboratory to another or from one city to another. This is because in most countries there are legal limits to the total weight of any given vehicle and its load which may be transported over public highways. As a result it has not heretofore been practicable or economically feasible to provide movable irradiation vehicles and apparatuses. Furthermore, where, as in the prior art, a labyrinth passage is necessary, the path along which any given package or container to be irradiated must move from the exterior into the exposure chamber, is neces sarily very long. As a result a large number of objects to be irradiated must be in the chamber at one and the same time in order to make the device economically feasible. This requirement is troublesome whenever it is required to change the products being exposed, when the time of irradiation must be changed, and when but a relatively few articles or packages are to be given a prescribed dosage.

In some prior art installations there are provided a number of discrete conveyors operating at different speeds in order to vary the time of exposure of two or more different products being irradiated simultaneously. Obviously such constructions introduce and require mechanism of excessive weight, complication and bulk.

The present invention eliminates and avoids the drawbacks of prior art methods and apparatuses just described. It enables the construction of an apparatus which is much lighter and less bulky for any given power of irradiation. The present invention also affords other advantages such as a simplified manner of operation easily adapted to automation for the carrying out of procedures over a certain period of time, without the attention of an operator. The invention also assures operation that is safe and free of danger to operating personnel.

The foregoing objects and advantages are attained by the steps hereinafter described, singly and in combination. The articles to be irradiated are enclosed in parallelepipedal containers which are then translated into a shielded rotatable enclosure or housing. This housing is rotated about an axis to place its loading opening in communication with the shielded exposure chamber. The articles are then translated in a path, one by one, in orderly sequence adjacent and about the radioactive material and are finally deposited into the shielded housing which is then rotated to enable the treated articles to be withdrawn for use. The articles so treated may be recirculated from the rotatable housing back into the chamber to repeat the cycle of exposure a certain number of times and thus to assure that each article or object has undergone the same time of exposure to rays from the source.

According to another feature of the invention, the irradiation of the products within the aforesaid containers is effected automatically by causing a certain number of the containers to traverse a closed path within and without the exposure chamber. The number of cycles thus performed by these containers is a function of the time required for each passage or cycle through the radiation zone, and the required total time of exposure.

The invention also has for a purpose an irradiation apparatus which is capable of carrying out the aforesaid steps and of providing the advantages thereto appurtenant, singly and in combination. The device includes an elongated shielded exposure chamber and means at one end of this chamber by which containers to be irradiated are introduced into the chamber for irradiation, and removed therefrom following irradiation.

More specifically, the means for introducing and removing the containers, as aforesaid, is composed of a rotatable housing having a vertical axis and four compartments with parallel axes, oppositely paired. The construction and arrangement are such that when two of the compartments open into and are in communication with the irradiation chamber, the remaining two open outwardly to the exterior thereof. The device or housing is rotatable in steps to thus place either pair of compartments in communication with the exposure chamber and, simultaneously, to place the other pair directed outwardly for loading and unloading.

The source of radiation consists of two, four, or more, usually four, plane panels which in inactive position are in side-by-side registration within a. removable shielded container and, in position for active radiation are spread apart for a more or less greater part of their height to thus span a total height substantially equal to the height or corresponding dimension of the objects to be irradiated. The source, namely, the aforesaid panels are located in a central-axial or vertical plane of the chamber when in active position. The total length of the panels is less than the corresponding dimension of the chamber, by a distance a little greater than the longitudinal dimension of the containers for the items to be irradiated, and about equal to the total overall length of two of the containers in .end-to-end contiguous relation. The panels are, as previously stated, located in the central vertical median plane of the chamber with a space on each side a little greater than the width of the containers.

Other features and advantages of the invention will become clear to those skilled in the art, after a study of the following detailed description i connection with the accompanying drawing.

In the drawing:

FIG. 1 is a plan view, partly in section, showing the general lay-out of an apparatus embodying the invention and by which the method thereof may be carried into practice;

FIG. 2 is a vertical longitudinal section through the apparatus in planes identified by the line 2-2, FIG. 1;

FIG. 3 is a vertical transverse sectional view taken in a plane identified by line 3-3, FIG. 2;

FIG. 4 is a vertical longitudinal sectional view taken in a plane identified by line 4-4 FIG. 3;

FIG. is an exploded detail view showing themechanism by which the panel of radioactive material is transferred from a shielded container detachably associated with the shielded irradiation chamber, out of such container and into operating position within the chamber;

FIG. 6 is an exploded detail view of the apparatus of FIG. 5, as viewed from the left; I 1

FIG. 7 is a perspective view of a modified form of the apparatus depicted upon FIGS. 5 and 6;

FIG. 8 is a sectional view of the apparatus of FIG. 7, taken in a plane identified by line 8-8, FIG. 7, and looking in the direction of the arrows;

FIG. 9 is a detail view to an enlarged scale, of one of the lower ends of two duplicate motor-driven shafts by which, the frames or panels of radioactive material are 7 raised and lowered into and from the exposure'chamber;

FIG. 10 is a perspective view from below, of a modified form of panel sections for the radioactive ampuls and means for associating and interconnecting the sections; and

FIG. 11 is a horizontal section takenin a plane identified by line 11-11,FIG. l0.

Referring in detail to the drawing, the irradiation chamber 10 has walls interconnected to enclose an elongated space. The walls are sheathed with lead. The interior transverse cross section'of the chamber is, as shown, essentially square and prolonged at one end to form a trapezoidal-shaped part. In plan, the chamber is of rectangular form and at one end, portions of the vertical side walls are shaped arcuately as indicated at 12 and 14, toconjointly define the surface of part of a cylinder having a vertical axis of symmetry 71 lying in the central or median vertical plane of the chamber. An element or housing 16 having thecross-sectional formv shown upon FIG. 1 is journaled on the aforesaid vertical axis for rotation in 180 steps between arcuate walls 12 and 14. This element is for the purpose of introducing products to be irradiated into the exposure chamber, and for withdrawing irradiated products therefrom. The housing which is of generally cylindrical form, is provided with vertical walls which define four compartments 20, 22, 24 and 26, having parallel lateral walls. These compartments are disposed in pairs'sov that each pair opens radially outwardly of the cylindrical housing at a respective side thereof diametrically opposite the other side.

The interior of the exposure or radiation chamber is divided centrally to form two parallel side corridors 28 and 30 symmetrically disposed upon opposite sidesof the central or median vertical plane of the chamber and separated by a space 32 for reception of the panels of radioactive ampuls. In the form shown upon FIGS. 1 to 4 there are two of these panels, 34 and 36 which when in operating position within the chamber are disposed in respective, laterally offset vertical contiguous planes, with one panel at an elevation above the other so that their combined heights span and register with the corresponding dimension of the containers C within the chamber. That is to say, the vertical dimension of each panel is substantially equal to half the corresponding dimension of the containers so when one panel is elevated above'the other so that its lower edge is substantially in registration with the upper edge of the lower panel, the combined height of the two is equal to that of the containers being irradiated. In operating position the respective vertical planes of the two panels are so closely adjacent that the irradiating effect of the panels is practically the same as though they were actually coplanar.

The floor of the exposure chamber is provided with conveyors. One conveyor translates the containers horizontally rearwardly in and along one corridor, longitudinally of the chamber, a second and retractable conveyor carries the containers horizontally and laterally at the rearward end of the chamber, from one corridor to the other, and transversely of the panels of radioactive material, and a third conveyor returns the containers along the other corridor to the forward end of the chamber or caisson. The conveyors may be alike and each may be in the form of a series of horizontal, horizontally-spaced rollers 38. The drive to the leading roller of each conveyor may be by a motor-driven chain extending about sprockets fixed coaxiallytherewith.

The products to be irradiated are placed in containers square or rectangular in cross section, each having a height which is about half of its length. Two other conveyors which may be of the same type and construction as those described in the preceding paragraph are horizontally disposed in parallel, side-by-side horizontally-spaced relation at the exterior of the exposure chamber for effecting loading and unloading. One of these conveys containers to be irradiated to and into the loading housing aforesaid. The other conveys containers which have been irradiated, away from the chamber The length, that is, the longitudinal horizontal dimension of the panels is a little less than the corresponding dimension of the containers to be irradiated. This relation assures the most efficient use of the radiation afforded by the source. For example, the'aforesaid length of the panels or source of irradiation may be a little different, preferably somewhat less by, say, about 30 percent, than the total overall length of three of the containers in end-to-end contact. As previously noted, the aforesaid second conveyor extends horizontally transversely across the exposure chamber at the rear end thereof. This conveyor whose rollers are identified at 40, enables the transfer of the containers, one-by-one, transversely of the exposure chamber, from onecorridor to the other.

Each conveyor is driven by a respective one of a plurality of electric motors 41 operating a chain 42, as aforesaid. The driving pinions of the chain are journaled upon the end of an arm 43 so that they-may be adjusted in the direction of prolongation of the chains.

The translation of containers in and along the corridors of the chamber is effected by the chains 42 driven by retractable spurs. Each chain has a total effective length equal to that of its corridor, plus the corresponding dimension of one of the compartments of cylinder 16. After rotation of the cylinder or housing so that a compartment thereof is adjacent the first container on the feed conveyor, this conveyor is operated to move the leading container into the loading compartment by force exerted by containers following. At the end of the return or exit corridor a device associated with principal chain 42 assures the movement of the leading container into the contiguous waiting compartment of the housing so that the housing can rotate without impediment.

The means thus disclosed for introducing containers into the caisson or exposure chamber, is simple, efficient and effective in operation and requires a weight of protective sheathing such as lead, considerably less than the prior art devices incorporating a labyrinth passage.

Each of the four compartments 20, 22', 24 and 26 provided in cylinder 16 which constitutes the housing, is of a size to receive and encompass one container. As previously noted, these compartments are arranged in pairs with those of each pair in side-by-side relation, each pair facing or opening outwardly diametrically opposite the other pair. The compartment of each pair when facing inwardly, that is, toward the caisson, is aligned with a respective one of the corridors thereof. The compartments are defined by intervening walls of lead whose. thickness is made sufficient to assure biological protection to personnel working about the apparatus. For example, with a source of radioactive cesium of 300,000 curies, the thickness of these walls is about I60 mm. of lead. The form and dimensions of the other walls of the cylinder are determined so that for all positions of rotation of the cylinder there is a thickness of lead between the interior exposure chamber and the exterior thereof, sufficient to prevent the escape of a dangerous degree of radiation.

The mobile or rotatable housing is supported by a stationery circular protective plate 69 of lead which acts to delimit the compartments at their bases. At the upper portion, protective from radiation is assured by a lead plate 70 which is a prolongation of the upper or roof portion of the irradiation chamber. The rotatable cylinder turns about its axis of symmetry 71, which has plate 69 as a base. For this purpose the plate is provided with a crown gear 72 fixed thereto and in mesh with a gear '73. The plate is mounted by means of conical rollers 74 for rotation about axis 71 and is driven by a variable speed electric motor 73. Releasable latch mechanism 80, FIG. 1, assures that the cylinder is stopped-precisely in positions which equiangularly spaced about axis 71, in this instance, 180. One of these 180 positions is shown upon FIG. 1.

source of radiation is transported in a container 911 table from and separately of the exposure chamber or caisson. Container 30 is mounted on wheels such as 31 which facilitate its emplacement in correct position beneath the chassis of the vehicle on which the exposure chamber and loading and unloading means are carried and transported. .iacits )2 serve to elevate the container into contact and operative relation with the entrance opening in the lower portion of the caisson.

The container for the radioactive panels, of which there are two in the model being described, consists essentially of a U- shaped enclosure 94 having thick walls 93, FIG. 2, of lead. A closure of generally cylindrical form fits within and is rotatable on its horizontally-disposed axis of symmetry within a cor respondingly-shaped opening in the top portion of the container.

This closure which is also of lead, has an axiallyand longitudinally-extending diametral slot which in a first position of rotation, as shown upon FIG. 3, is in registration with the opening in the container and so enables the radioactive panels to be elevated out of the container and into the exposure chamber. In a second position at 90 to the first position the closure completely obturates the opening and thus affords biological protection to operating personnel when the panels are within the container. Rotation of the closure between the two 90 positions aforesaid, is effected manually by a lever 95. 01" course, suitable stops, not shown, are provided to assure that the closure is not rotated beyond the two correct 90 positions. Because of the separability of the container for the radioactive panels from the caisson, the two items may be transported separately in two loads and thus correspondingly reduce the weight of each load. Thus an apparatus of much greater capacity may be made in mobile form than would otherwise be possible.

The panels 34, 36 constituting the source of radioactivity are disposed in parallel side-by-side relation within the separabie container. When the apparatus is to be prepared for operation, these panels are elevated out of the container and into the exposure chamber where, as previously noted, they are vertically offset in respective but closely adjacent planes centraliy of the chamber.

Mechanism is provided to extract the panels from their container when the latter is properly attached to the caisson, and ciosure 94 has been rotated to open position, and to elevate them into operating position within the chamber. This mechanism consists essentially of vertical threaded shafts 98, F165. 4), 5 and 6, which extend upwardly through the roof of the caisson and through guides Hi2, 1132a, FIG. 4. These threaded shafts carry internally threaded pinions 189, 1690, respectively, which are rotated in unison by means of bevel pinions 11 and 13 fixed to the respective ends of a shaft 15. See FEGS. 5 and 6. This shaft is journaled in bearings mounted on base 17 carried by the roof portion of the caisson and is connected for rotation by motor 112 operating through reduction gearing. The upper ends of shafts 98, 9&1 are square and engage within correspondingly shaped openings in cross bar M6. The shafts are thus prevented from rotation. Suitable such as keys engaging in transverse slots in the square of the hold the bar thereto. Thus, rotation of motor 111?. in one direction or the other causes a corresponding vertical translation of the shafts in unison. At their lower ends shafts are reduced in diameter as indicated at 122, 122a. c ends are threaded and engage in respective threaded see 124 124:: in upper bar 129 forming support means for panel 36, FIG. 5.

A pair of vertical rods 126, 126a pass with a smooth sliding fit through respective bores 128, 123a in the ends of the upper support bar 131 of panel 34. Each rod has a head or enlargement at its lower end. When, in upward axial movement these heads 136, 136a, engage bar 131 they act to raise the panel therewith. At their upper ends these rods enter bores 130, 130a in the respective ends of upper bar 129 of panel 36 and are fixed thereto by screws 18 and 19 threaded into the ends of the rods. During the first part of the vertical translation of shafts 98, 98a, panel 36 only is correspondingly elevated. But when in the course of continued elevation of this panel into the exposure chamber, heads 136, 136a engage bar 131 and thereafter panel 34 is also elevated and the two panels move upwardly in unison. The construction and relation of parts is such that at the instant panel 34 begins to elevate, the lower edge of panel 36 is in substantial registration with the upper edge of panel 34. Hence when the two panels are fully and properly emplaced within the chamber, their radiation effect is the same as that of a single panel equal to their combined areas and vertical dimensions.

The circuit including elevating motor 112 includes a limit switch 132, FIG. 2, which has a first pair of normally-closed contacts and a second pair-of contacts which are normally open. The first pair of contacts are in circuit with motor 112 so that when panel 36 reaches proper elevation within the chamber, the end of its bar 129 engages and operates the toggle of switch 132 thereby stopping the motor. At the same time the normally-open contacts of switch 132 are closed. These contacts are in circuit with a relay which controls a relay having a secondary circuit in series with a second and normally-closed switch 133, FIG. 2, so located that when and if panel 34 has been elevated to proper position within the exposure chamber, the end of its support bar 131 engages and opens this switch. The aforesaid secondary circuit includes a danger signal lamp which, in a manner clear from the preceding description is lighted only if panel 34 has not been fully elevated into the chamber and into correct operating position therein. The operator is thereby advised when in the operation of motor 112, both panels are in correctly elevated, operating position.

An ionization chamber 134 is located within a bore or recess in the roof of the chamber and is connected with logarithmic amplifier 135 provided with a number of terminals capable of and connected to operate respective relays. These relays are independently adjustable to be responsive to different levels of radioactivity incident upon chamber 134. For example, as shown upon FIG. 3, there may be three relays each controlling a respective one of signals 136, 137, 138. The relay controlling signal 136 is responsive to a very low level of radioactive emanation and one which is not dangerous. The second signal 137 is operated in response to a higher level of emanation as, for example, that produced when container is moved into the position shown upon FIGS. 3 and 4, closure 94 is open but the panels are still within their container. The third signal 133 is actuated in response to a still higher level of emanation such as that extant when the panels have been fully emplaced within the exposure chamber, as depicted upon FIG. 2. The circuit which operates signal 138 is also connected over line 1441, KG. 3, with an electromagneticallyoperated plunger, not shown, normally spring-pressed to lock housing 16 or, more specifically, its base plate 69. The plunger is normally urged into locking position and is withdrawn only by and in response to energization of its electromagnet. Thus it is impossible to emplace or introduce containers to be irradiated within the exposure chamber, unless and until panels 34, 36 are fully and correctly located within this chamber. This construction makes it impossible for housing 16 to be inadvertently turned, with consequent dangerous exposure to radiation from the interior of the chamber by unauthorized entry thereinto.

The aforesaid circuits and indicators give complete protection against danger from inadvertent operation of the apparatus and exposure to a dangerous level of radiation. Switch R32 assures an indication of proper elevation and positioning of upper panel 36, and opens the circuit of motor 112 when such positioning has been attained. Likewise the operator is fully and definitely advised unless lower panel 34 has been properly elevated and positioned.

As a further precaution to advise when the radioactive panels have been fully lowered into their container 90, there is provided in this container, as shown upon FIG. 4, a switch 144. This switch is so located as to be closed only when upper panel 36 has been completely lowered into the container. This switch is in circuit with a signal located on a control table or board before the operator. When the signal is energized the operator is advised that both panels are fully located within their container 90 and that lever 95 may be safely operated to turn closure 94. The circuit of switch 144 is also associated with another switch 1%, FIG. 4, and which is closed only by and in response to movement of the container into proper mating relation with chamber 10, as depicted upon FIGS. 3 and d. An electromagnetic lock 148 is mounted on container 9%) adjacent a projecting pintle fixed with closure 94, and is operable thereon to permit rotation of the closure only when the two switches 11 M, 146 are activated. Hence closure 94 may be rotated only when (a) container 90 is in the position shown upon FIGS. 3 and i, with respect to chamber and (b) both panels are in fully lowered position within this container.

The apparatus is easily adapted to either manual or automatic operation. In manual operation the containers to be irradiated are placed, one by one, within a compartment such as 20, FIG. 1, and the housing is rotated 180. Since the irradiated container at the forward end of the corridor has been moved by device 43 into compartment 24 the aforesaid 180 rotation exposes this container for unloading or for recirculation as previously described. Thus, at each 180 rotation of the housing one container is positioned for movement into the exposure chamber and an irradiated container is exposed for unloading. Of course, where recirculation of the containers is to be effected, the exposed container must be transported from, say, compartment to compartment 26, before the housing is given its next 180 rotation. This is done simply by means of the two longitudinally-disposed, parallel conveyors 42 and the single transverse conveyor, as clearly shown upon FIG. 1, it being understood that these will be loaded with containers as shown upon FIG. 2. Thus each container, in turn, is retracted out of compartment 20, moved rearwardly on and along one longitudinal conveyor, then on the transverse conveyor, then forwardly on the other longitudinal conveyor into compartment 26 where, on 180 rotation of the housing it is positioned ready for direct advancement into the first corridor of the exposure chamber. Consideration of FIG. It shows that for any given cycle the side of each container which is next to the wall of the chamber in its passage in and along the first corridor, is next to the source panels in its return passage along the second corridor. This results in a more even and uniform irradiation of each container. By recycling, each container a selected number of times the dosage of irradiation of articles therein may be raised to a desired level.

It is thus possible to improve the utility of the apparatus and method by providing extra containers for each cycle. This manner of operation enables a more uniform dosage for each container and the articles therein, especially the four containers which are located at the two extremities of each corridor. These containers are in the positions noted, not directly exposed to the source, so that radiation received by them is weaker than that received by the containers at the other six positions. Thus the distribution of radiation is not uniform. However, the dosage received by each container during each cycle is the same, so that it may suffice to run each through a single cycle only by regulating the time of the cycle in accordance with the desired dosage of the articles or materials within the containers.

in accordance with automatic operation, where recycling is to be effected, the chamber is filled with a number of containers C, eight in the model shown. In addition a number of supervise are positioned on the exterior conveyors, as shown upon FIG. 2. An automatic control device, not shown, is provided which rotates housing 16 through in timed relation with movement of containers into and out of the compartments 20, 22, etc., so that each passes through a desired number of cycles. In such a manner of operation the speed of passage of the containers is not critical because all of them pass a certain number of times through the radiation chamber. This manner of use frees the operator for an extended period of time and enables one person to supervise a number of apparatuses or to direct his attention to other duties.

In order to assure homogeneity of the dosage of radiation over the upper and lower portions of the containers, the source comprising panels 34, $6, has a height such that when extended as shown upon FIG. 2, they extend above and below the levels of the tops and bottoms of the containers, respectively. An overall excess in the vertical dimension of the panels, of about 15 percent affords a satisfactory homogeneity of dosage. This does not require an excessive increase in overall height of the apparatus In fact, since the two panels which constitute the source are disposed in side-by-side, closely-spaced registration when within the container in which they are transported from place to place, the added height of the panels when extended is not excessive. The dimensions of the exposure chamber are thus not necessarily unduly augmented by the additional height of the panels when extended, as aforesaid and as shown upon FIG. 2, because the chamber must have the added vertical dimension anyway in order to accommodate the conveyor roller, chains, etc. Furthermore, near the top of the chamber the small additional height is afforded by the arched form of the roof structure, in both transverse and longitudinal directions.

Where it is desired or necessary to use panels of a smaller total or extended height, it is possible nevertheless to assure good homogeneity of irradiation dosages by making the containers of, say, one-half the vertical dimension of those shown, and cycling them through the exposure chamber in superposed layers. At the end of a cycles, the containers are rearranged so that those that those previously forming the top layer now form the lower layer, and vice versa. By thus passing the containers through a number of pairs of cycles, uniformity of dosage is assured even although the extended panels have an overall height less than thoseshown upon FIG. 2.

FIGS. 7, 8 and 9 show a modified form of means for supporting and extending the panels, and which is of particular use in cases where the height of the containers to be irradiated is materially less than the total extended vertical dimension of the combined panels, so that it is possible to employ the panels at less then their maximum combined dimension. Thus with the modification being described, the panels may be used in apparatus having an exposure chamber, for example, with a vertical dimension not sufficient to accommodate the panels when fully extended.

For this purpose the upper panel consists of an upper supporting plate 48 having a U-shaped frame 46 secured to and depending from its lower surface. The legs of this frame are provided with regularly and vertically space, verticallycoplanar openings which form opposed pairs, each supporting a respective one of radioactive ampuls one of which is identified at 45. 1

Likewise the lower panel consists of an upper support plate 59 having U-shaped frame d7 secured to and depending from its lower surface and also provided with holes for supporting a number of ampuls or tubes 45, in vertically-spaced coplanar relation. As shown upon FIG. 8, plate 59 is notched at 63 to accommodate frame 4t: with a loose fit.

A pair of vertical, laterally-spaced, parallel shafts and 47 may be disposed and rotated in the same way and by the same mechanism as are shown upon FIGS. 2, 4 and d, for rotating shafts 98 and 9&1. Referring in detail to FIG. 9, the lower end of shaft 46 is shown to have a first relatively long upper threaded portion Mia and a shorter lower threaded portion 660. The two threaded portions are of the same diameter and pitch, and are separated by a smooth cylindrical portion 46b of lesser diameter. The axial length of this smooth portion is determined by the desired partial separation or extension between the two panels. The lower end of shaft 47 is formed to be identical to that of shaft 46, as just described.

Upper plate 46 has threaded holes 51 and 52, respectively, spaced to simultaneously receive the respective lower threaded ends of shaf s 46, 4'7, when the latter are lowered into contact therewith and subsequently rotated. Conical guides 53 and 54 assure that the ends of the shaft are guided into the desired threading relation with the threaded holes.

A pair of guide rods 55 and 56 have their upper ends fixed, as by threading, to upper plate 48. These rods extend downwardly and each passes with a smooth sliding fit through a respective one of holes 57 and 58 in lower support plate 59. Thus the two plates are interconnected for smooth relative, guided, vertical movement. The lower ends of rods 55 and 56 are enlarged so that when upper panel 43 has been raised to the limit, relatively to lower panel 44, that is, to the position shown upon FIG. 7, further elevation results in the two panels moving upwardly as a unit.

Support plate 59 has a threaded apertures 60, 61 g each directly below and vertically aligned with a respective one of threaded apertures 51, 52. When, as-in the case of the model shown upon FIGS. 1 to 6, the radioactive panels are to be elevated out of their container to their fully extended position, shafts 46, 47 are lowered as previously described, and turned until each threads into its aperture 51, 52. Thereafter the shafts are elevated and panel 43 moves upwardly alone until the headed lower ends of rods 55 and 56 engage the lower surface of plate 59. Thereafter on continued elevation of shafts d6, 67, the two panels move upwardly as a unit into final emplaced position within the exposure chamber.

When it is desired to emplace the panels in the chamber at less than their fully extended position or relation, shafts 46, 47 are lowered as usual and rotated until the lower threaded portions such as 46c, pass completely through holes 51, 52. Rotation is continued until these threaded ends such as 46c also pass completely through threaded holes 60 and 61, respectively, in panel support plate 59. At the same time the threaded portions of rods 46, 47, such as 46a are threadedly engaged within apertures 51 and 52; but since portion 46a, is of greater axial length than portion 46c, these latter portions have passed completely through apertures 60, 61 while portions 46a, etc. are still threadedly engaged within holes 51, 52.

when portions 46c have passed downwardly completely through apertures 66, 61, rotation of shafts 46, 47 is stopped and they are translated upwardly in unison. Panel 43 first rises a distance substantially equal to the axial dimension of smooth unthreaded portions 46b. Then the threaded ends 46c engage holes 66, 61 below plate 59 and thus cause panel 44 to rise also. Thereafter the two panels rnove upwardly as a unit into emplaced position within the exposure chamber.

in this way the panels may be used in connection with an exposure chamber having an interior height less than the one depicted upon FIGS. 1 to 6; or, alternatively, the panels may be used in a chamber of standard or usual height as in FIGS. 1 to 6, to irradiate containers having a vertical dimension corresponding to the combined vertical dimension of the panels when only partially extended, as just explained. In both cases the panels may be restored into collapsed relation within their shipping or storage container by procedures the reverse of that set forth.

FTGS. l6 and 11 show a modified form of the radioactive panel assembly which gives improved uniformity of radiation.

FlG. shows the fully extended position of the panels as they are disposed for use within the radiation chamber, as and similarly to that shown in FlG. 2. The panels are in four sections 66, 65, 66 and 67, of about the same size and effective area. As described in connection with FIGS. 1 to 6, each of these sections includes a number of ampuls or tubes 68 containing radioactive material and mounted in horizontal, vertically-spaced, parallel, coplanar relation in a U-shaped metal frame such as that identified at 75. The assembly of four panel sections includes an upper support plate 76 and is maintained in erect and expanded position within the exposure chamber by means of two shafts which may be the same shafts as those depicted upon FIGS. 2 through 6 and hence are identified by the same reference characters 98, 98a. The lower threaded ends of these shafts are positioned and arranged to engage respective threaded holes 77 and 79 in plate 76. Conical guides 81, 82 fixed with plate 76 about the holes therein, act to guide the ends of the shafts when lowered, into registration with the holes. Then, when the shafts are rotated in synchronism, as by means previously described in connection with FIGS. 2, 4 and 5, they thread into the holes and are subsequently translated vertically to expand the panels and then to elevate them out of their container and into the exposure chamber.

The U-shaped panel sections 64 and 65 have the upper ends of their legs attached to the under side of plate 76. As clearly shown upon FIG. 11, these sections are offset in mutually normal horizontal directions. Four rods 83, 84, 85 and 86 have their upper ends fixed in plate 76 and depend therefrom in spaced parallel relation, as is well shown upon FIGS. 10 and 11. Panel section 66 includes an upper support plate 87 which has holes receiving rods 83 and 85 with a smooth sliding fit. Likewise upper support plate 88 of panel section 67 has holes which receive rods 84 and 86 with a smooth sliding fit. All four rods are provided at their lowe ends with abutments which engage the lower surfaces of the respective plates 87, 88 and assure that the four panels move upwardly as a unit when they are in the relation shown upon FIG. 10. In the position depicted, upper sections 64, 65 are at the left and right, respectively, of plate 76, but section 65 is offset rearwardly of section 64 in a contiguous parallel plane. Section 67 is immediately below section 65 but offset forwardly thereof and in the same plane as section 64. Section 66 is immediately below section 64 but offset rearwardly thereof and is coplanar with section 65. See also FIG. 1 l.

The arrangement is such that when in the expanded position of FIG. 10 the radioactive tubes subtend an effective area about equal to the combined areas of the panels. When the panel assembly is in collapsed condition for storage and transport, within its container, lower panels 66, 67 are in their uppermost positions of translation on and along rods 83, etc., in which position section 66 registers with and lies behind section 64, and section 67 overlies and registers with section 65. The overlap as shown upon FIG. 11 assures that when the panels are in expanded relation the radiation from each unit of area of the total area subtended is substantially the same and uniform.

Thus, in a manner clear from the preceding description, when a panel of the type shown on FIGS. 10 and I1 is mounted within the exposure chamber, similarly to FIG. 2, each container and the articles or materials therein receive the same average dosage for each pass thereof adjacent and parallel to the panel.

While the panel has been shown in four sections it may be made in a larger number of sections of equal size and in multiples of four, provided each pair of sections consists of an upper and a lower unit parallel with and offset the same distance forwardly and rearwardly, respectively, of a common medianvertical plane. Thus the average radiation received by each container in a pass adjacent the panel will be essentially the same for each increment of area of the container projected upon the median plane of the panel.

In some cases it may be desirable to use the panel with an extended height of about half that available when the panels are fully extended. This is desirable, for example, to give objects in or near the horizontal median plane of the containers a larger dosage of radiation than objects more remote from this plane, above or below. Such a disposition is easily obtained by use of the invention of FIGS. 7, 8 and 9, by making shaft sections 46b very short. Then, when shaft sections 46c are completely threaded through holes 60, 61, the two panels will be in substantial registration when raised by shafts 46, 47 into operating position within the exposure chamber; and articles passing in the median horizontal plane of the superposed sections will receive a more powerful dosage of radiation than articles or material more remote from this plane on either side thereof.

We have thus disclosed a method and apparatus fulfilling all of the objects stated, and which is of great utility in the uniform, safe, efficient, rapid and low cost irradiation of objects, articles and materials. Due to the separability of the radioactive container from the exposure chamber, mobility of the apparatus is greatly facilitated so that it may be readily moved from place to place and easily assembled and disassembled. Thus a single apparatus embodying our invention may fulfill the needs for a number of separate prior art apparatuses, each at a different location. The safety features incorporated into the invention make certain that the parts may be safely assembled and taken apart and that the apparatus when assembled is operated correctly, all without danger to operating personnel.

it will be understood that bar 116 is removable from shafts 98, 923a, etc., and, when so removed, that the shafts may be individually and manually rotated to cause their lower ends to thread into apertures 124, lZda, respectively. After this, bar 116 is replaced and motor 112 is energized to rotate the shafts in unison and to thereby translate the panel out of its container and into operating position within the exposure chamber. In the same way, shafts 46, 47, FIGS. 7 and 9, may be individually rotated to effect engagement of threaded portions such as 460 into holes 51, 52 only or, alternatively, to thread these portions completely through holes 60, 61, as and for the purposes previously explained.

While we have disclosed the form of apparatus and method of operation presently preferred by us, numerous changes, modifications, substitutions, rearrangements of parts, and variations in manner of use will readily occur to those skilled in the art, after a study of the foregoing disclosure. Hence the disclosure is to be taken in a purely illustrative rather than a limiting sense; and it is our desire and intention to reserve all changes within the scope of the subjoined claims.

We claim:

ll. The method of irradiation of articles and materials enclosed within containers, comprising, positioning an essentially plane panel of radioactive material within and centrally of a shielded chamber, translating the containers along a first fixed path in the chamber contiguous to and parallel with one face of the panel, for exposure to radiation therefrom, then in translation normal to said first path, transversely of the panel, and return in a second fixed path of translation, contiguous to and along the other face of the panel, to complete a cycle wherein opposite sides of the containers are equally exposed to radiation from the panel.

2. The method of claim 1, said containers being of parallelepipedal form'and passing along said paths in end-to-end contiguous relation.

3. The method of claim 1, and at the terminus of said second path, rotating each container in sequence 180", then recirculating said containers in a second cycle as aforesaid, to thereby assure equal exposure of all articles within the containers.

2-. The method of claim 3, said first and second paths being horizontal and horizontally spaced, said rotation being about an essentially vertical axis.

5. The method of irradiation of articles enclosed within containers of regular geometrical form, comprising, positioning an essentially plane panel of radioactive material in a central vertical plane within a shielded chamber, to define first and second horizontal parallel corridors in the chamber on respective sides of the panel and translating the containers to be irradiated in sequence, in a first fixed path in and along said first corridor in proximity to and parallel with said panel on one side thereof, then transversely translating the containers in sequence across one end of the panel and return in a second .1 2 fixed path of translation along the second said corridor, in parallel proximity to the panel and on the other side thereof, to thus complete a cycle wherein opposite sides of the containers are equally exposed to radiation from the panel.

6. The method of claim 5, and adjusting the vertical dimension of the panel to about the same as the corresponding dimension of the containers, whereby all articles therein receive essentially the same dosage of radioactivity during each cycle.

7. The method of claim 5, and adjusting the vertical dimension of the panel to a dimension materially less than the corresponding dimension of the containers, whereby each article therein receives a dosage for each cycle, proportional to its distance above or below a horizontal median plane through the panel.

8. In an apparatus for irradiation of containers enclosing articles and materials to be made radioactive, a shielded chamber having top, bottom and sidewalls, and an end wall, means for positioning an essentially plane panel of radioactive material vertically and centrally in said chamber between said said walls, to define first and second parallel corridors on respectively opposite sides of a panel therein, a turnable shielded housing closing the otherwise open end of said chamber and rotatable to position a container at the entrance to said first corridor and to receive a container at the exit from said second corridor, and conveyor means in said chamber, operable to convey containers in translation and in contiguous sequence in and along a first path along said first corridor, in parallel proximity to said panel on one side thereof, then transversely of said panel adjacent said end wall, then in a return and second path along said second corridor in parallel proximity to said panel on the other side thereof, to thereby complete a cycle.

9. The apparatus of claim 8, said housing being of generally cylindrical form and turnable about a vertical axis of symmetry, said housing having walls defining diametrically opposite, outwardly-opening pairs of discrete compartments, each compartment of a pair registering with a respective one of said corridors when the housing is in a respective one of two positions of rotation about said axis.

10. The apparatus of claim 8, said bottom of said chamber having a central longitudinal opening in a plane between said corridors, a shielded panel container having an upwardly-facing opening, and means to move said container into contact with said bottom, with said openings in registration, said container being separable from said chamber and separately transportable.

11. The apparatus of claim 10, and closure means carried by said panel container and operable to seal the opening therein.

12. The apparatus of claim 11, said closure means being generally cylindrical and journaled horizontally in the top of said container, said closure means having a longitudinally and diametrically-extending slot which in a first position of rotation obturates the opening in said container, and in a second position of rotation registers with said opening.

13. The apparatus of claim l2, and means to prevent rotation of said closure means between first and second positions unless (a) said container is in sealing contact with said bottom and (b) said panel is fully emplaced within said container.

14. The apparatus of claim it), a panel of radioactive material in said container, and means carried by said chamber and movable through the opening therein to engage and elevate said panel out of said container and into said chamber.

15. The apparatus of claim 1%, said last-named means comprising first and second vertical shafts spaced longitudinally of said chamber and extending through the roof thereof, said shafts being threaded at their lower ends, means operable upon said shafts to axially. and vertically translate the same in unison into contact with said panel, and means operable to rotate said shafts synchronously to engage the threaded ends thereof with threaded apertures in said panel.

16. The apparatus of claim is, said last-named means being operable to translate said shafts vertically in unison to elevate said panel out of said container and into operating position within said chamber. 7

17. in an apparatus for irradiating objects and materials with radioactive emanation, a panel comprising first and second discrete sections each generally rectangular and each adapted to support radioactive material over the area thereof, means mounting and interconnecting said sections for relative guided movement from a first collapsed relation wherein said sections are in substantial fully overlapping relation in respective contiguous, offset, parallel planes, to a second extended relation wherein said sections are offset each in its said plane and with the top edge of one section substantially in registration with the bottom edge of the other said section.

8. The apparatus of claim 17, said first section comprising, a first plate, a U-shaped frame secured to and depending from said first plate, first and second rods each secured at one end to said plate and depending therefrom in laterally-spaced parallel relation, said second section comprising a second plate, a U-shaped frame secured to and depending from said second plate, said second plate having a pair of apertures through which said rods respectively and slidably extend, and abutments at the lower ends of said rods and engageable with said second plate to determine the fully extended relation of said sections.

19. The apparatus of claim 18, said first and second plates each having two, laterally-spaced threaded holes, each hole of one plate being in vertical alignment with, and forming a pair with, a corresponding hole of the other plate, first and second vertical shafts each in alignment with a respective pair of holes and having first and second axially-spaced threaded portions on its end for engagement within the threads of said holes, and means for rotating said shafts to thread the first threaded sections of said shafts each through a respective pair of holes and simultaneously to thread the second threaded sections into the holes of said first plate, whereby, on vertical translation of said shafts in unison, said first and second panel sections are offset by the distance of separation only of said first and second threaded portions of said shafts.

20. The apparatus of claim 17, said first section comprising a support plate, first and second U-shaped frames secured to and depending from said plate in respective first and second laterally-and longitudinally-offset, contiguous, parallel planes, said second section comprising third and fourth rectangular frames, means mounting said third frame to said plate for translation relatively thereto and in said first plane, from a first position in substantial registration with said second frame, to a second position offset therebelow, means mounting said fourth frame to said plate for translation relatively thereto and in said second plane, from a first position in substantial registration with said first frame, to a second position offset therebelow, and means limiting the offset of said third and fourth frames to positions with their top edges substantially in registration with the bottom edges of said first and second frames, respectively, all said frames being adapted to support radioactive material.

21. The apparatus of claim 20, said first and fourth frames being mounted to said plate in side-by-side contiguous relation with said second and third frames. 

1. The method of irradiation of articles and materials enclosed within containers, comprising, positioning an essentially plane panel of radioactive material within and centrally of a shielded chamber, translating the containers along a first fixed path in the chamber contiguous to and parallel with one face of the panel, for exposure to radiation therefrom, then in translation normal to said first path, transversely of the panel, and return in a second fixed path of translation, contiguous to and along the other face of the panel, to complete a cycle wherein opposite sides of the containers are equally exposed to radiation from the panel.
 2. The method of claim 1, said containers being of parallelepipedal form and passing along said paths in end-to-end contiguous relation.
 3. The method of claim 1, and at the terminus of said second path, rotating each container in sequence 180*, then recirculating said containers in a second cycle as aforesaid, to thereby assure equal exposure of all articles within the containers.
 4. The method of claim 3, said first and second paths being horizontal and horizontally spaced, said rotation being about an essentially vertical axis.
 5. The method of irradiation of articles enclosed within containers of regular geometrical form, comprising, positioning an essentially plane panel of radioactive material in a central vertical plane within a shielded chamber, to define first and second horizontal parallel corridors in the chamber on respective sides of the panel and translating the containers to be irradiated in sequence, in a first fixed path in and along said first corridor in proximity to and parallel with said panel on one side thereof, then transversely translating the containers in sequence across one end of the panel and return in a second fixed path of translation along the second said corridor, in parallel proximity to the panel and on the other side thereof, to thus complete a cycle wherein opposite sides of the containers are equally exposed to radiation from the panel.
 6. The method of claim 5, and adjusting the vertical dimension of the panel to about the same as the corresponding dimension of the containers, whereby all articles therein receive essentially the same dosage of radioactivity during each cycle.
 7. The method of claim 5, and adjusting the vertical dimension of the panel to a dimension materially less than the corresponding dimension of the containers, whereby each article therein receives a dosage for each cycle, proportional to its distance above or below a horizontal median plane through the panel.
 8. In an apparatus for irradiation of containers enclosing articles and materials to be made radioactive, a shielded chamber having top, bottom and sidewalls, and an end wall, means for positioning an essentially plane panel of radioactive material vertically and centrally in said chamber between said said walls, to define first and second parallel corridors on respectively opposite sides of a panel therein, a turnable shielded housing closing the otherwise open end of said chamber and rotatable to position a container at the entrance to said first corridor and to receive a container at the exit from said second corridor, and conveyor means in said chamber, operable to convey containers in translation and in contiguous sequence in and along a first path along said first corridor, in parallel proximity to said panel on one side thereof, then transversely of said panel adjacent said end wall, then in a return and second path along said second corridor in parallel proximity to said panel on the other side thereof, to thereby complete a cycle.
 9. The apparatus of claim 8, said housing being of generally cylindrical form and turnable about a vertical axis of symmetry, said housing having walls defining diametrically opposite, outwardly-opening pairs of discrete compartments, each compartment of a pair registering with a respective one of said corridors when the housing is in a respective one of two 180* positions of rotation about said axis.
 10. The apparatus of claim 8, said bottom of said chamber having a central longitudinal opening in a plane between said corridors, a shielded panel container having an upwardly-facing opening, and means to move said container into contact with said bottom, with said openings in registration, said container being separable from said chamber and separately transportable.
 11. The apparatus of claim 10, and closure means carried by said panel container and operable to seal the opening therein.
 12. The apparatus of claim 11, said closure means being generally cylindrical and journaled horizontally in the top of said container, said closure means having a longitudinally- and diametrically-extending slot which in a first position of rotation obturates the opening in said container, and in a second position of rotation registers with said opening.
 13. The apparatus of claim 12, and means to prevent rotation of said closure means between first and second positions unless (a) said container is in sealing contact with said bottom and (b) said panel is fully emplaced within said container.
 14. The apparatus of claim 10, a panel of radioactive material in said container, and means carried by said chamber and movable through the opening therein to engage and elevate said panel out of said container and into said chamber.
 15. The apparatus of claim 14, said last-named means comprising first and second vertical shafts spaced longitudinally of said chamber and extending through the roof thereof, said shafts being threaded at their lower ends, means operable upon said shafts to axially and vertically translate the same in unison into contact with said panel, and means operable to rotate said shafts synchronously to engage the threaded ends thereof with threaded apertures in said panel.
 16. The apparatus of claim 15, said last-named means being operable to translate said shafts vertically in unison to elevate said panel out of said container and into operating position within said chamber.
 17. In an apparatus for irradiating objects and materials with radioactive emanation, a panel comprising first and second discrete sections each generally rectangular and each adapted to support radioactive material over the area thereof, means mounting and interconnecting said sections for relative guided movement from a first collapsed relation wherein said sections are in substantial fully overlapping relation in respective contiguous, offset, parallel planes, to a second extended relation wherein said sections are offset each in its said plane and with the top edge of one section substantially in registration with the bottom edge of the other said section.
 18. The apparatus of claim 17, said first section comprising, a first plate, a U-shaped frame secured to and depending from said first plate, first and second rods each secured at one end to said plate and depending therefrom in laterally-spaced parallel relation, said second section comprising a second plate, a U-shaped frame secured to and depending from said second plate, said second plate having a pair of apertures through which said rods respectively and slidably extend, and abutments at the lower ends of said rods and engageable with said second plate to determine the fully extended relation of said sections.
 19. The apparatus of claim 18, said first and second plates each having two, laterally-spaced threaded holes, each hole of one plate being in vertical alignment with, and forming a pair with, a corresponding hole of the other plate, first and second vertical shafts each in alignment with a respective pair of holes and having first and second axially-spaced threaded portions on its end for engagement within the threads of said holes, and means for rotating said shafts to thread the first threaded sections of said shafts each through a respective pair of holes and simultaneously to thread the second threaded sections into the holes of said first plate, whereby, on vertical translation of said shafts in unison, said first and second panel sections are offset by the distance of separation only of said first and second threaded portions of said shafts.
 20. The apparatus of claim 17, said first section comprising a support plate, first and second U-shaped frames secured to and depending from said plate in respective first and second laterally-and longitudinally-offset, contiguous, parallel planes, said second section comprising third and fourth rectangular frames, means mounting said third frame to said plate for translation relatively thereto and in said first plane, from a first position in substantial registration with said second frame, to a second position offset therebelow, means mounting said fourth frame to said plate for translation relatively thereto and in said second plane, from a first position in substantial registration with said first frame, to a second position offset therebelow, and means limiting the offset of said third and fourth frames to positions with their top edges substantially in registration with the bottom edges of said first and second frames, respectively, all said frames being adapted to support radioactive material.
 21. The apparatus of claim 20, said first and fourth frames being mounted to said plate in side-by-side contiguous relation with said second and third frames. 